Surface Chemical Functionalization Of Oxide Free Si111 Surfaces And Silicon Nitride

Amination of surfaces is useful in a variety of fields, ranging from device manufacturing to biological applications. Previous silicon amination studies have concentrated on the ammonia vapor dissociation on silicon surfaces, with considerably less work done using liquid phase ammonia. Bifunctional molecules such as diamines are particularly attractive for surface amination since they can form different surface structures. In contrast to ammonia modification of silicon surfaces, direct grafting of diamine molecules to silicon is almost nonexistent in literature. Therefore in this dissertation, the study of amination of silicon surfaces using liquid phase ammonia and diamine reactions will be done. The approach used to study these complex liquid systems involves a systematic set of well-defined surfaces (oxide-free H-, 1/3 monolayer (ML) F- and Cl-terminated Si(111)), chosen for their atomic roughness and single reaction site. This systematic set is instrumental for achieving our goal of fundamentally understanding the reaction mechanisms and surface reactions in liquid phase. Results show that amines and diamines physisorb on the H-terminated Si(111) surface and chemisorb on the 1/3 ML F- and Cl-terminated surfaces, with full removal of the chlorine observed. Both studies showed evidence of oxidation or oxynitride formation, and surprisingly, Si-H bond formation on the previously hydrogen-free Cl-terminated Si(111) surface, which is attributed to a step edge reaction in the case of ammonia and a chlorine-proton exchange in the case of ethylenediamine. On stoichiometric silicon nitride surfaces, we find that HF etching leads to etchant salt formation if not immediately water rinsed. A salt-free HF-etched silicon nitride surface contained coverages of various terminations including: ~70% ML fluorine, ~40% ML hydroxide and ~20% ML amine. Selective functionalization of silicon nitride over oxide surfaces was achieved by using a Schiff base reaction, involving the conversion of the amine surface groups to imines using undecanal. These results illustrate the need and relevance of in-situ characterization to fully exploit semiconductor and oxide surfaces. A better understanding of the surface reaction mechanisms can provide the scientific community a deeper understanding of the reaction outcomes on these different surfaces, and in the future could aid in the development of silicon surface modifications.